Molecular oxygen is widely used in many industries and in many processes such as steel production, glass making, wastewater treatment, and in energy production via chemical oxidation and combustion processes. While the use of pure molecular oxygen is desirable, the separation and storage of molecular oxygen has been heretofore difficult, hazardous, and expensive.
Cryogenic distillation, the liquefaction and rectification of air, is commonly used to separate oxygen from other gases to obtain high purity oxygen. This process, however, is inefficient and costly unless performed on a very large scale. Electrolysis of water is energy intensive, and results in the production of by-product hydrogen. Chemical oxygen separation processes, such as those using an oxygen acceptor and/or an oxygen scavenger, require the use of corrosive chemicals.
An oxygen separation method described in U.S. Pat. No. 4,738,760 to Marianowski et al., is the electrochemical separation of oxygen from oxygen containing gaseous mixtures, such as air, using a molten nitrate salt electrolyte retained in a porous matrix between two gas porous catalytic electrodes. U.S. Pat. No. 5,007,992 to Weber, describes a method of oxygen separation using an electrolytic ceramic cell made of partially stabilized zirconia, which when activated by heat and an electric current, selectively transports oxygen.
The separation of gases by membranes has been proposed but most membranes are not practical because of low selectivity. Polymer membranes can be used to separate oxygen from air but the oxygen concentration that can be obtained with their use is limited to between 30 to 40%.
Oxygen is separated for use in situ in some instances by methods which employ a gas impermeable membrane capable of conducting oxygen ions and oxygen electrons. Generally, these membranes are comprised of metal oxide or ceramic materials and operate at varying temperatures and pressures.
The use of electrochemical membranes that are gas tight and selective to oxygen are described in European Patent Application No. 90 111,503 (EP Publication 405,288) and in Japanese Patent Application No. 54 - 169,462 (Kokai 56-92,103). These describe the use of a dense ceramic membrane that conducts both oxygen ions and electrons to separate pure oxygen from air. The solid membrane is disposed between a gas with a high concentration of oxygen (air) from a gas with a low concentration of oxygen (helium or a vacuum).
In such membrane systems, the gradient in oxygen concentration provides the driving force for the separation. Oxygen molecules at the air side of the membrane take up electrons to form oxygen ions, and the ions migrate through the membrane to the low concentration (He or vacuum) side of the membrane. The oxygen ions then give up their electrons to form molecular oxygen and the electrons migrate back to the air side of the membrane.
U.S. Pat. Nos. 5,240,473, 5,240,480, 5,261,932, and 5,269,822 teach oxygen ion transport membranes comprising multicomponent metallic oxides. Similarly, U.S. Pat. No. 5,273,628 to Liu et al. teaches an oxygen separation membrane comprised of bismuth oxide and ceria based ceramic materials in a variety of forms, and U.S. Pat. No. 5,108,465 to Bauer et al. teaches a membrane comprised of ceramics which can conduct both electrons and oxygen ions.
Materials having both electronic conductivity and oxygen ion conductivity are described in U.S. Pat. No. 4,330,633 to Yoshisato et al, and in Japanese patent publications 61-21717, 58-64258, 57-160967, 57-145070, and 57-123833.
U.S. Pat. No. 5,035,727 to Chen describes oxygen extraction by passing hot, compressed air over a solid electrolyte membrane selective to the permeation of oxygen and applying an external voltage across the membrane surface.
European Patent Application No. 399,833 by Mazanec et al describes oxygen separation using an electrochemical reactor cell having a solid multi-component membrane for conducting oxygen ions and electrons.
The disclosure of the above listed patents and patent applications are hereby incorporated by reference, as if fully written out hereinbelow.
A drawback of the above mentioned technologies is the difficulty in the fabrication of a gas-tight ceramic reactor. The most common reactor designs proposed are similar to a tube or a plate heat exchanger. High temperature seals for these apparatus represent a particular challenge. Large tube or plates of oxygen transport membranes are difficult to fabricate due to the brittleness of the material. Further, in operation, both the temperature and oxygen gradients across the membrane create stresses across the material.
Regarding the use of molecular oxygen, once molecular oxygen has been separated and concentrated, the storage and delivery (including transport) of high purity oxygen is also problematic and hazardous. The art does not teach the use of a single article for the combined separating, storing, and delivering of substantially pure molecular oxygen.
Thus, it is an object of the present invention to provide an article for separating, storing, and delivering substantially pure oxygen. It is another object of the present invention to provide a method for separating, storing, transporting, and delivering substantially pure oxygen. It is yet another object to provide an apparatus for the separation and utilization of substantially pure oxygen.